Iran live updates: Strait of Hormuz shut until Tehran's conditions met, Ghalibaf says

The State Department posted a security alert on Saturday evening advising Americans currently in the Middle East to "exercise heightened vigilance" and "be aware of potential flight cancellations, airspace closures, and travel disruptions."

"Iranian-supported Houthis have engaged in hostilities against Saudi Arabia, including civilian airports. This military conflict has the potential to escalate rapidly," the post said.

The alert also advised Americans outside the Middle East to "seriously reconsider travel to and through the region."

-ABC News' Lauren Minore

Iranian National Security Council Secretary General Mohsen Rezaei said in an interview with Al Jazeera on Saturday that Tehran wants an end to the war between Saudi Arabia and Yemen.

Talking about Iran’s nuclear program, Rezaei said the Islamic Republic remains "committed" to the former leader’s fatwa on its nuclear doctrine, which had prohibited the manufacture of a nuclear weapon. However, he said he does not know "what will happen in the future."

“We have not yet made a decision to withdraw from the NPT," said Rezaei, referring to the Treaty on the Non-Proliferation of Nuclear Weapons. He added that "this matter depends on Washington’s conduct."

He told Al Jazeera that Iran's conditions have been conveyed to the U.S. via mediators, Qatar and Pakistan. They include the lifting of a U.S. naval blockade and an end to the war on all fronts, as he said.

-ABC News' Somayeh Malekian

Saudi-led coalition spokesperson Major General Turki Al-Maliki said Saturday that Saudi air defenses intercepted a Houthi ballistic missile fired toward Riyadh.

In a statement posted on social media, al-Maliki said the Royal Saudi Air Defense Forces had "successfully intercepted and destroyed" a ballistic missile launched by the Houthis toward the Saudi capital at dawn.

The statement said the targeting of civilians and civilian infrastructure in Riyadh demonstrated what it described as the Houthis' "hostile and terrorist behavior."

Al-Maliki also said the Houthis attempted to target civilians and civilian sites in Yanbu, Baish, Taif and Farasan, but that all attacks were thwarted by Saudi air defense systems.

The statement did not mention any attack on Riyadh's international airport.

-ABC News' Jamie Dorrington

The Houthis issued a statement Saturday via a military spokesperson, saying they attacked what they called "sensitive sites in the Saudi capital, Riyadh" and Aramaco facilities in Yanbu, western Saudi Arabia, with ballistic missiles and drones.

Video from earlier in the day showed black smoke rising near the international airport in Riyadh. Saudi Arabia hasn't immediately commented about the Houthi's claims.

The Houthi statement reads the two military operations were in response to "continued aggression of the criminal Saudi enemy" and Saudi Arabia's "criminal attempts to target the capital, Sana'a, using ISIS-style tactics, including indiscriminate bombings targeting civilians."

-ABC News' Jamie Dorrington